Jean-Claude Juncker wants to review a scheme that lets the public suggest new laws after campaigners called for gay marriage to be explicitly unrecognised in EU law.

His officials are alarmed that a petitions system designed to make the EU more democratic could boost euroscepticism and have negative “political consequences” for the European project.

A campaign poster in Ireland encourages voters to say no to same-sex marriage in the referendum held there in May 2015 Photo: PAUL FAITH/AFP/Getty Images

Campaigners, backed by Christian lobby groups, have demanded a change to European law to state that marriage exists only between men and women - a “family” should be defined strictly as a heterosexual married couple and their descendants, they argue.

They hope to use a scheme backed by Mr Juncker and established in 2012 that obliges the EU to consider proposed new laws if they get the backing of one million citizens.

At a meeting of the European Commission, members of Mr Juncker’s inner circle expressed alarm that the Citizens’ Initiative scheme is being used for “emotionally charged” topics that will not “move the European project forward”.

They were told by the EU’s chief lawyer that there were no legal grounds for rejecting the proposed petition, entitled: “Mum, dad and kids - European citizens' initiative to protect Marriage and Family.”

The minutes disclose: “During the ensuing discussion, the Members (i) regretted that experience to date had shown that citizens’ initiatives did not always move European law or the European project forward, but tended instead to involve highly controversial and emotionally charged issues of greater interest to minorities than to the vast majority of EU citizens and, ultimately, generated euroscepticism."

They go on to say the members "(ii) called for a debate on how to rectify this situation and (iii) stressed that, in the current European context, the Commission should take account of the political consequences that this mechanism could have in the longer term.”

The minutes record Mr Juncker, the Commission president, “was in favour of discussing these matters at the Commission seminar to be held early in 2016”.

The European Citizens’ Initiative scheme was introduced in 2012, and invites the public to suggest new laws.

If campaigners can collect one million signatures from across at least seven member states within a year, the campaigners are invited to a hearing in the European Parliament and the Commission must respond, either by drawing up legislation or explaining why there are no grounds to do so.

EU sources insisted Mr Juncker is committed to the scheme, and denied he is planning to water it down. One idea being explored is to promote it more widely so that groups other than special interest lobbyists and special interest groups come up with ideas, they said.

Jean-Claude Juncker has called for a review of the initiative to let voters suggest new EU laws Photo: AP

But Paul Moynan, the director of the Christian lobbying group Care for Europe, who helped organise the petition, said he was angered by the Commissioners' "clearly preposterous" reaction.

“The European citizens' initiative process was created to give direct initiating power to ordinary Europeans,” he said. “It is regrettable and undemocratic that the Commission seems to begrudge any initiative that does not fit their political agenda.”

Having been approved by the EU, the petition will open for signatures later this month. It does not seek to change law at a national level, but the concept of marriage and the family is used widely in cross-border EU law on issues such as access to benefits and human rights.

Mr Moynan said recognising a traditional formulation of the family at a European level would help address Europe’s low birth rate. The petition says that many European voters are "very uncomfortable" at the introduction of same-sex marriage.

No petition has so far resulted in a change in the law. Previous campaigns that successfully collected one million signatures include a call to protect water supplies from privatisation, a ban on vivisection and the outlawing of human embryo research.

Mr Juncker’s officials have been alarmed by an apparent “contagion” of anti-EU movements across the continents, with referendums held or scheduled in Britain, Denmark and the Netherlands. There are fears that states such as Poland and Hungary, who were thought to have embraced liberal values on joining the EU a decade ago, are drifting towards the populist right.

Same-sex marriages are currently recognised in 9 of 28 EU states: Belgium, Denmark, France, Ireland, Luxembourg, the Netherlands, Spain, Sweden, and the UK. Finland will follow from 2017.

Civil partnerships, granting legal recognition of relationships but falling short of marriage, are recognised in all states except Bulgaria, Cyprus, Greece, Latvia, Lithuania, Italy, Poland, Portugal, Romania and Slovakia.

In several states, including Poland, Hungary and Bulgaria, marriage is defined as between one man and one woman in the constitution, presenting a significant obstacle to reform.

Some members of Mr Juncker's team want same-sex marriages conducted in one country to be recognised by a second EU state, even where those states do not conduct them.